1. Field
One or more embodiments herein relate to a magnetoresistive memory device.
2. Description of the Related Art
A magnetic tunnel junction (MTJ) element may be used to form a memory cell. A read operation for an MTJ element is performed by a magnetic resistance effect with perpendicular magnetization. One type of MTJ element includes a magnetic tunnel junction layer having an insulating layer between a free layer and a reference layer. The magnetization direction of the free layer is variable, while the reference layer maintains a predetermined magnetization direction.
In a memory using the MTJ element, a switching current (minimum write current) may decrease at high temperatures. For example, the write current may decrease by about 10% at 75° C. As a result, an unselected memory cell may be disturbed if the write current at room temperature (e.g., 25° C.) is used at high temperature without modification.
Since the current driving capability of a write current source circuit itself decreases as a temperature increases, the write current may decreases to some extent. However, the write current may not decrease as much as the switching current decreases. The switching current due to high temperature markedly decreases according to miniaturization of a memory cell, thereby causing a significant decrease in write margin.
Also, read margin may decrease due to high temperature in a read operation, e.g., an MTJ element may have voltage dependency and temperature dependency. Accordingly, since a magnetoresistive (MR) ratio and a current difference also have temperature dependency, the read margin may decrease as temperature increases.
In a magnetoresistive random access memory (MRAM) device, since a read current is a tunnel current between magnetic materials, an increase in a temperature causes both a decrease in magnetization of a magnetic film and an increase in a tunnel probability due to thermal excitement. Since the tunnel current increases and the MR ratio sharply decreases, read margin decreases. The decrease in read margin significantly depends on temperature due to miniaturization of a memory cell.